Elements of natural philosophy (Volume 2-3) . atio of the velocities through theirrespective ethers. Hence, both the absolute and rela-tive indices vary with the wave lengths, being greatestin lavender grey and least in red, those of violet, indigo,is greatest for blue, green, yellow, and orange, lying intermediate be- lavender grey .1 o ,, * .A tween these. ana least for red. Effect of an When, therefore, the waves which constitute white of wwte Hght!* %k* fall obliquely and simultaneously upon the face ofa new medium, they will all be deviated on account ofthe change of density and elasticit
Elements of natural philosophy (Volume 2-3) . atio of the velocities through theirrespective ethers. Hence, both the absolute and rela-tive indices vary with the wave lengths, being greatestin lavender grey and least in red, those of violet, indigo,is greatest for blue, green, yellow, and orange, lying intermediate be- lavender grey .1 o ,, * .A tween these. ana least for red. Effect of an When, therefore, the waves which constitute white of wwte Hght!* %k* fall obliquely and simultaneously upon the face ofa new medium, they will all be deviated on account ofthe change of density and elasticity of the ether whichthey then encounter, and the intromitted waves will beunequally deviated, because of their difference of wavelength; these waves will, hence, separate from each otherand proceed in different directions; and, if intercepted byany reflecting surface, as a screen, will exhibit thereontheir respective colors. ELEMENTS OF OPTICS. 295 110. This is well illustrated by the action of an opti- Experimental illncfrnfinn • Fig. illustration; cal prism. Let abeam S S\ of solarlio-hLbe admitted in-to a dark roomthrough a small holeiii a window shutter,and received upon ascreen X Y\ it willexhibit a round lu-minous spot at T, in the direction of SS produced; but if the face of a re-fracting prism A B C, be interposed, the spot Twill dis-appear, and there will be formed upon the screenan elongated image of the sun, variously and beautifully Hg^JuJdt0colored, beginning with red on the side of the refract-pass through a , , • prism; ing angle A, ol the prism, and passing m successionthrough orange, yellow, green, Hue, indigo, and terminat-ing in violet and lavender grey, making eight in colors are not separated by well-defined bounda- colors produced;ries, but run imperceptibly into each other ; nor are thecolored spaces of the same length. The following tableexhibits the relative lengths of these spaces as obtainedby Sir IsAxVc Newton with the glass prism
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